Once you get used to going through long stretches of time without eating, intermittent fasting (IF) seems like a great way to lose weight and maintain it. There are other health benefits, too, such as improved digestion, more energy, and improved insulin levels. When your body goes through periods of fasting, it boosts the production of growth hormone, which helps you lose weight and gain muscle. While there are several different ways to do IF, the main tenets are still the same: periods of eating interspersed with periods of fasting.
But what do you eat during your feeding window? Technically, intermittent fasting just refers to when you eat, not how much you eat. "There are no rules about how much you should eat when you are not fasting," Julie Upton, MS, RD told POPSUGAR. "The diet was designed so that the fasting period creates the caloric deficit so that you can lose weight."
In fact, Kristen Mancinelli, MS, RDN, author of the book Jump Start Ketosis: Intermittent Fasting for Burning Fat and Losing Weight, said she doesn't tell her clients to count calories. Instead, she advises them to eat until they feel satisfied. Since people who follow the 16:8 (leangains) plan typically only eat two meals a day, they will naturally eat fewer calories since once they have acclimated to the fasting period, they tend to not get hungry outside of their feeding window.
However some people think eating on IF gives them licence to throw caution to the wind and eat as much as they want. If weight loss is your goal, you need to still be mindful of how many calories you are ingesting. After all, you can't fast for 16 hours and then eat 5,000 calories during your eight-hour feeding window and still expect to lose weight.
"Formally, calorie needs will remain the same as with any other diet plan, and differ based on the person's frame size, gender, starting weight, goal weight, and activity level," Mancinelli told POPSUGAR. To calculate what your calorie target is to lose weight, use this equation. Just make sure you aren't going below 1,200 calories a day. The only exception is if you are doing the 5:2 method: five days a week you eat normally (for example, 2,000 calories a day) and two days a week on your fasting days, you eat only 20-25 percent of your average calories (so 400 to 500 calories). Even if weight loss is your goal, you don't need to eat in a calorie deficit on your feeding days; those 2,000 calories should still yield weight loss results along with the other two fasting days a week. Over the course of the week, this creates and average daily calorie deficit.
Whether you are doing the 16:8, 5:2, or some other variation of IF, you should still eat whole, unprocessed foods during your feeding window. To reap the benefits of intermittent fasting, stick to fruits and vegetables, whole grains, lean protein, and limited sugar and refined carbohydrates. Of course you can enjoy treats on occasion; just make sure they only make up 20 percent of your diet. Eventually, your body will get used to this way of eating and naturally crave healthy food.
"People are surprised that they don't gorge on their eating days or during their eating window after they've been fasting for a while," Mancinelli said. "One of the things intermittent fasting teaches you is how to notice and respond to hunger and satiety signals. So, rather than counting calories, practitioners can respond to their body's natural signals; it's very freeing!"